fix(bootstrap_sdk): Use the latest SDK tarball as a fallback seed.
fix(bootstrap_sdk): Use the latest SDK tarball as a fallback seed.

When running bootstrap_sdk for the first time on a host the default of
using a previous catalyst run as a seed won't work but this may be a
fresh SDK install so that tarball is probably around somewhere and will
work as a default seed for most things.

trnubo/scripts,crawford/scripts,fivethreeo/scripts,mischief/scripts,mjg59/scripts,andrejro/coreos--scripts,marineam/coreos-scripts,mischief/scripts,BugRoger/scripts,fivethreeo/scripts,fivethreeo/scripts,nicescale/scripts,smilart/scripts,zhang0137/scripts,gtank/scripts,sigma/coreos-scripts,glevand/coreos--scripts,bcwaldon/coreos-scripts,coreos/scripts,vmware/coreos-scripts,glevand/coreos--scripts,trnubo/scripts,smilart/scripts,marineam/coreos-scripts,endocode/scripts,nicescale/scripts,vmware/coreos-scripts,andrejro/coreos--scripts,coreos/scripts,andrejro/coreos--scripts,endocode/scripts,marineam/coreos-scripts,bcwaldon/coreos-scripts,mischief/scripts,smilart/scripts,nicescale/scripts,zhang0137/scripts,mjg59/scripts,gtank/scripts,zhang0137/scripts,endocode/scripts,mjg59/scripts,vmware/coreos-scripts,crawford/scripts,bcwaldon/coreos-scripts,gtank/scripts,sigma/coreos-scripts,sigma/coreos-scripts,BugRoger/scripts,trnubo/scripts,crawford/scripts,BugRoger/scripts